Field of the Invention
The present invention relates to an organic light emitting display device, and more particularly, to an organic light emitting display device which is capable of reducing operating voltage and improving emission efficiency.
Discussion of the Related Art
Image displays used for displaying a variety of information on the screen are one of the core technologies of the information and communication era. Such image displays have been developed to be thinner, lighter, and more portable, and furthermore to have high performance. With the development of the information society, various demands for display devices are on the rise. To meet these demands, research on panel displays such as liquid crystal displays (LCD), plasma display panels (PDP), electroluminescent displays (ELD), field emission displays (FED), organic light emitting diodes (OLED), etc., is actively under way.
Among these types of panel displays, the OLED devices are a type of devices that, when a charge is injected into an organic light emitting layer formed between an anode and a cathode, emit light as electron-hole pairs are produced and dissipated. The OLED devices are advantageous in that they can be formed on a flexible transparent substrate such as plastic, can be driven at relatively low voltage, less power consumption, and excellent colors sensitivity, as compared to plasma display panels or inorganic EL displays. Especially, white OLED devices are used for various purposes in lighting, thin light sources, backlights for liquid crystal displays, or full-color displays employing color filters.
An organic light emitting display device may be formed by sequentially stacking an anode, a hole injection layer, a hole transport layer, an light emitting layer, an electron transport layer, an electron injection layer, and a cathode. Accordingly, a hole-electron pair, formed by the recombination of a hole supplied from the anode and an electron received from the cathode, forms an exciton, and light emission occurs by an energy generated as the exciton returns to the ground state.
However, if the electron transport layer of an organic light emitting display device according to the related art has a high triplet exciton energy level, the operating voltage rises due to low electron injectability and low electron mobility. Also, if the electron transport layer has high electron injectability and electron affinity, the charge balance is broken due to high electron mobility, thus decreasing lifetime and efficiency.